Step 2: Find the leaks

Step 3: Leak Found!

Here is one leak - a pinhole in the weld where I had previously repaired the cracked manifold. I had loads of leaks, leaking manifold, cracks in both ...

I have had an exhaust leak on my trusty Skoda for a while, I can hear it coming from miles away!

My problem was that to find the leak with the engine running was too difficult as the manifold and downpipe heated so quickly that I didn't have time to find the leak before everything was too hot to touch.

My solution, the mighty power of the humble vacuum!

WORDS OF WISDOM
1) Make sure the whole exhaust system is completely cold before starting work - I ended up quite ill after burning my hand on my friends exhaust many years ago.
2) Don't forget to disconnect the vacuum before starting the engine

Step 1: Connect the vaccum cleaner

This step is easy, just duck tape the pipe of the vacuum to the tail pipe of the exhaust and switch on.

I have used a Dyson cleaner which has an effective bypass valve to stop the motor overheating when the machine gets blocked. If you use a vacuum which does not have a good bypass, then you might need to make a deliberately leaky connection to the exhaust to stop the motor in the vacuum overheating.

Step 2: Find the leaks

Now use a stethoscope (a funnel jammed in the end of a piece of flexible tube) to listen for leaks.

To find a leak play the open end of the hose as closely as you can over the exhaust system, paying particular attention to parts which might leak (Joints, flexible sections, etc.).
As you move the hose over a leak you will hear the nature of the hissing sound change.The suspected leak can then be confirmed by pressing your finger over the area and listening for the hissing to disappear.

Thanks for the great tip!! I decided to use my vacuum's blower function instead and just felt/listened for blowing air. I would guess if you weren't careful the blowing air could cause some ear damage, but that's why we're careful! This was so much better than having someone rev the engine while I listened and felt around for hot air blowing out.

i think you can also use a manual air pump to blow in , of course with the use of the washing up liquid. i wonder if just by obstructing the exhaust, it can create a pressure to obtain a good clue where to concentrate your attention.

New downpipe for most of the holes, but a little bit of welding on the manifold.(I do the welding with the engine hot (not running because you need to disconnect the electrics) and this helps to avoid heat stress cracking around the weld)

IIRC cast iron is tough to weld. They usually do a pre-heat with torches and hammer on the weld while it cools. Also, there's a special type of arc electrode for cast iron that is expensive because of a high nickel content.

Yes the main trick with cast iron is to pre-heat (blow-lamp or bake - this is what getting the exhaust up to temperature does) and then cool slowly - often burying in sand or wrapping up. I have done a bit of cast iron welding, repairing an old wood-burning stove and the manifold and it seems to work OK.I don't have a special electrode - I just use my MIG welder with standard steel wirePete

Great post. Would it be a bad idea to use a shop vac and blow air into the tailpipe? I dont know if this would be bad for the catalytic converter or not. But if you did that then you could simple feel the leaks with your hand and probably wouldn't need the funnel contraption.

You could try blowing - I couldn't do that because the Dyson doesn’t have a blowing attachment.I don't think you would be able to find the tiny leaks just by feeling, but you could try a bit of washing up liquid and look for bubbles